In the field of high-speed printing devices which are especially suitable for use in connection with electronic data processing systems, the wire matrix type of printer has come into increasing use. In this type of printer, letters, numbers and symbols are formed from a series of dots produced by the impact of the ends of a plurality of wire elements on record media, most customarily in combination with an ink ribbon which provides the ink needed to produce a mark on the record medium being printed upon.
Since the wires employed in the matrix printer have a short operating stroke, it is important that a uniform distance be maintained between the print head and the upper surface of the medium being printed upon. It is therefore important, in those cases in which a plurality of different thicknesses of record media may be printed upon by a matrix printer, to provide a compensating device which acts to maintain the same relative distance between the print head and the upper surface of the record media regardless of changes in the thickness of the record media.
In order to maximize efficiency and economy of operation in wire matrix printers it is also important to obtain the maximum utilization of the ink ribbon which is employed with the printer, and to prevent excessive wear in any one area of the ribbon. It is thus quite advantageous, in those instances in which the width of the ribbon exceeds the corresponding dimension of the character being printed, to provide means whereby different transverse portions of the ribbon can be employed during printing, so that the entire ribbon is used in a relatively uniform manner, and the frequency of changing of the ribbon can be reduced.
Various compensation devices for maintaining a predetermined distance between the print head and the record media regardless of the thickness of the record media are known in the prior art. For example, the German Offenlegungsschrift No. 2246243 and Auslegeschrift No. 2321017 both utilize an arrangement in which print head guide rollers are run along a flexible tape secured at its ends. However in those arrangements the tape and print head must be raised for insertion and movement of the paper, owing to the lateral instability of the unsupported central portions of the tape. Another patent showing the use of a flexible tape on which a forms compensator sensing device rides in U.S. Pat. No. 3,750,792. Again in this patent, the arrangement of elements is not such that the record media can be conveniently inserted without movement of the tape. Other patent references showing various printing arrangements are U.S. Pat. Nos. 1,988,189; 3,720,298; 3,904,018; and 3,990,560; and the German Offenlegungsschrift No. 2318947.